Phased array system

ABSTRACT

A phased array antenna utilizing a parasitic reflector in which the area of the array of radiating elements is smaller than the area of the reflector. The reflector has a concave surface which, in one embodiment of the invention, is a hyperbola of revolution for collimating the rays of radiation incident thereupon from the array of radiating elements. The surface of the reflector is particularly adapted to permit the generation of a set of phase shift command signals by means of a novel ray tracing program to provide a collimated beam which may be scanned in response to the phase shift imparted through radiation radiated by the radiating elements. A narrow beam of radiation is obtained by virtue of the relatively large sized reflector even though the dimensions of the array of radiating elements are relatively small.

ilnited States Patent Heeren et a1.

[ 11 Nov. 27, 1973 PHASED ARRAY SYSTEM [75] Inventors: Vernon L. Heeren, Wayland; James M. Howell, Hudson; C. Dale Reis,

Boxborough, all of Mass.

21 Appl. No.: 186,128

[52] U.S. Cl 343/100 SA, 343/754, 343/854 [51] Int. Cl. H01 3/26 [58] Field of Search 343/100 SA, 854,

343/754, 776-779, 112 TC, 16 R, 6.5 R

[56] References Cited UNITED STATES PATENTS 3,652,978 3/1972 Halliday et a1 343/100 SA 3,569,976 3/1971 Korvin et al.... 343/779 3,170,158 2/1965 Rotman 343/100 SA 3,484,784 12/1969 McLeod, Jr. 343/100 SA 3,611,401 10/1971 Connolly 343/100 SA 3,106,708 10/1963 Sletten 343/16 R 3,564,543 2/1971 Nehama et al.. 343/6.5 R 3,001,193 9/1961 Marie 343/16 R X COORDINATE CONVERTER 6/1969 Alfandari et a]. 343/16 R 7/1969 Hannan 343/779 Primary Examiner-Benjamin A. Borchelt Assistant Examiner-Richard E. Berger Attorney-Milton D. Bartlett et a1.

[5 7] ABSTRACT A phased array antenna utilizing a parasitic reflector in which the area of the array of radiating elements is smaller than the area of the refllector. The reflector has a concave surface which, in one embodiment of the invention, is a hyperbola of revolution for collimating the rays of radiation incident thereupon from the array of radiating elements. The surface of the reflector is particularly adapted to permit the generation of a set of phase shift command signals by means of a novel ray tracing program to provide a collimated beam which may be scanned in response to the phase shift imparted through radiation radiated by the radiating elements. A narrow beam of radiation is obtained by virtue of the relatively large sized reflector even though the dimensions of the array of radiating elements are relatively small.

24 Claims, 14 Drawing Figures E d l3? a e ma I ELECTRONIC umr 50 42 F 78 k m i M 1 ELEV ow Z 1 WAVE AJMUTH DIFF 510 I PROC i GATING j l ANGLE H2 1 REF 1 MITTER N3 02 I U6" //6 1 i l SYSTEM I I TIMING PATENTED RSV 2 7 E373 SHEET l 0F 8 TOP OF LENS NO TEMP COMP IO-l2 TEMP RISE 40 GS S CoMP C O 8-IO TEMP RISE O o O O O 06 45 COMP O O 0 48/2 0 O O O O \D O O O O O O O O O O O 6-8 TEMP RISE LIPS CDMP O 3.5 6" TEMP RISE BOTTOM OF LENS A B A B L a L. I L E. LL LHL/Lm. L l l I l I I I I T I I 'gF 0 90 660-1000 g CHANGE PHASE SIGNALS TRANSMITTED OF PHASE To AND RECEIvED FRoM SHIFTERS 4s AIRCRAFT 34 OF FIG.I 0F FIG. I

COMPUTER 86 OF COMPUTER 86 FIG I COMPUTES NEXT /3 OF PROV'DES DIRECTION OF BEAM 56 ANGLE DATA ON LINE H8 PHASE SHIFT 0F PHASE WITH RESPECT TO SHIFTERS 48 0F DIRECTION OF FIG. I REMAINS FIXED BEAM 56 PHASED ARRAY SYSTEM The invention herein described was made in the course of or under a contract or subcontract thereunder with the Department of Defense.

BACKGROUND OF THE INVENTION This invention relates to antennas utilizing a parasitic reflector and, more particularly, to an electronically scanned phased array antenna in which the scanned radiation is reflected from the parasitic reflector.

In the past, phased array antennas have utilized a large number of elements. For example, 11,000 elements may be utilized for such an antenna providing a narrow beam on the order of one degree beamwidth which can be scanned through an angle of :60 degrees. Such an antenna is ideally suited for multiple target tracking of targets varying widely in their elevation and azimuth angles. As is well known, such antennas are excessively expensive, excessively large and heavy, and excessively complex for implementation in typical commercial applications, such as the guiding of aircraft along an airport runway. However, except for the foregoing disadvantages, a phased array antenna is ideally suited for guiding aircraft along an airport runwaysince such aircraft can be seen by the radar even when they are displaced from the desired approach path; the antenna may remain stationary while generating tracking beams in a variety of directions to intercept the various aircraft. It is also apparent that the standard form of phased array radar antenna has greater tracking capability, namely, substantially larger azimuthal and elevation tracking capability, than is necessary for situations such as the aforementioned guiding of aircraft along an airport runway.

SUMMARY OF THE INVENTION The aforementioned deficiency in the utilization of phased array radars for applications such as the guiding of aircraft along an airport runway is overcome by an antenna, in accordance with the invention, which utilizes substantially fewer radiating elements than that utilized in the standard form of phased array antenna, approximately 800 radiating elements being used in the preferred embodiment of the invention as compared to approximately 1 1,000 of these radiating elements which would be required by a standard form of phased array antenna providing an equivalent beamwidth. To obtain a narrow beam from a relatively small array of radiating elements, a passive element such as a large reflector or lens is utilized wherein the dimensions of the passive element are sufficiently large to provide a narrow beamwidth. A large reflector has been utilized in the preferred embodiment. There is also disclosed a system comprising the novel antenna for guiding vehicles, particularly aircraft, along a predetermined path such as an airport runway.

A suitable geometry is established which permits the generation of phase shift commands for controlling the phases of radiation radiated from each of the respective elements of the array in a manner which permits this radiation to be scanned across the surface of the reflector at a variety of angles and be reflected therefrom in the desired narrow beam, and yet retain the beam shape and form of the active radiating aperture. One such surface which has been found to provide a suitable geometry to permit this operation of the antenna is a conic surface, particularly the hyperbola of revolution (or hyperboloid), and accordingly, the reflector of the preferred embodiment has a surface described as a hyperbola of revolution. A ray tracing program, valid for all forms of radiant electromagnetic energy as well as acoustic energy, is disclosed which enables computer generated signals to select the requisite phase shift for each radiating element in a manner conforming to the geometry of the positions of the radiating elements relative to the reflector such that a limited scan narrow beam phased array antenna is obtained. It has also been found that the array of radiating elements should be located along a preferably spherical surface or, simply a cylindrical surface, to facilitate the formation of the scannign radiation beam.

It is interesting tonote that, with respect to a preferred embodiment of the invention, while phase shift commands are provided which deflect the wavefront of radiation radiated by the aforesaid radiating elements by as much as approximately degrees, the direction of the beam of radiation emanating from the re flector is deflected only :10 degrees because of the concave surface of the reflector of the preferred embodiment and the positions of the radiating elements relative to this surface. Thus, the antenna of this invention has the effect of demagnifying the scanning angle of rays of radiation while magnifying the radiating aperture and directivity from that which could be provided by the array of radiating elements itself.

BRIEF DESCRIPTION OF THE DRAWINGS The aforementioned features and other advantages of the invention are explained in the following description taken in connection with the accompanying drawings wherein:

FIG. 1 is a pictorial view of a radar tracking system utilizing an antenna in accordance with the invention and further showing portions of the radar system in block diagram form;

FIG. 2 is an alternative embodiment of the invention wherein a passive reflector is repflaced with a passive lens;

FIG. 3 is a further embodiment of the invention in which an active lens comprising a plurality of phase shifters is replaced with an active reflector element similarly comprising a plurality of phase shifters;

FIG. 4 shows the interelement geometry utilized in calculating mathematical expressions to be utilized by the computer of the system of FIG. 1 for developing phase shift commands for the phase shifters in the an tenna of FIG. 1;

FIGS. 5 and 6 show two forms of active aperture distortion caused by improperly matching the curved sur face of a reflector to the wavefront, or isophase surface, of radiation incident from a subarray of phase shifters of FIG. 1 upon the reflector;

FIGS. 7A and 7B show the spacings and dimensions of the components of the antenna of the invention as used in the preferred embodiment in, respectively, a top view and a side view;

FIG. 8 shows a geometric construction useful in a ray tracing program for the determination of coefficients in a computer phase shift control program for the steering of a beam of radiation for the antenna of the invention;

FIG. 9 is a block diagram of a beam steering unit utilized for generating phase shifter control signals for steering a beam of. radiation for the antenna of the invention;

FIG. is a schematic diagram of a phase shifter drive circuit for the phase shifters in the antenna of the invention;

FIG. 11 is a timing diagram of signals utilized in the drive circuit of FIG. 10;

FIG. 12 is a diagrammatic frontal view of a lens of the antenna of the invention showing a distribution of heating within the lens and the width of pulses used to apply additional flux to magnetic material of phase shifters utilized in the lens to compensate for the effect of the differential heating of the phase shifters; and

FIG. 13 is a timing diagram of the system of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, there is shown a system 30 for obtaining a data relative to a source of radiation comprising an antenna 32 in accordance with the invention, here shown tracking a source of radiation, namely, an aircraft 34 which is landing on a runway 36 adjacent the antenna 32. The antenna 32 comprises, in this embodiment of the invention, a reflector 38, a lens 40 and a horn 42, the horn 42 transmitting radiation through the lens 40 towards the reflector 38 for reflection therefrom to the aircraft 34. The reflector 38 is substantially larger than a region illuminated by the radiation 44, such a region hereinafter being referred to as an active aperture 46, to permit the active aperture 46 to be scanned about the reflector 38. In addition, the active aperture 46 is larger than the lens 40 to provide a narrow beam of radiation and increased directivity for the antenna 32. The surface of the reflector 38 is curved in a manner to be described which, in accordance with the invention, provides substantially equally shaped active apertures 46 having substantially equal illumination patterns as viewed along the axis of a beam of radiation emanating therefrom independently of the locations of these active apertures 46 upon the reflector 38. Such equality of the active apertures 46 is most desirable for obtaining precise data on the positions and trajectories of aircraft, such as the aircraft 34, which are landing on the runway 36.

The lens 40 comprises regions which introduce varying amounts of phase shift to incident radiation, these phase shifting regions being accomplished by a plurality of phase shifters 48 disposed normally to the inner and outer arcuate surfaces 50 and 52 of the lens 40. The horn 42 is spaced from the lens 40 such that an arcuate wavefront emanating from the horn 42 upon reaching the lens 40 preferably coincides approximately with the inner arcuate surface 50. Energy is coupled from this wavefront into each of the phase shifters 48 and propagates through the phase shifters 48 to reradiate from the outer surface 52 of the lens 40. The phase shifters 48 are preferably of the latching type utilizing a fern'te material having a substantially square shaped hysteresis curve such that electrical signals for controlling these phase shifters need be applied along the lines 54 only momentarily to adjust the phase imparted to energy propagating through each phase shifter 48 and, thereafter, each phase shifter 48 retains the phase shift until further signals are applied along the lines 54. For example, the phase shifter 48 may comprise a pair of windings positioned around the ferrite material such that one of these windings is used to reset the ferrite material to a reference state of magnetization while the second winding is energized with a voltage pulse of a predetermined duration for establishing a state of magnetization to the ferrite material to give the desired phase shift. This will be described further hereinafter with reference to FIG. 10.

Phase shift signals, to be described hereinafter, are applied along the lines 54 to adjust the phase shifts of each of the phase shifters 48 such that radiant energy emanating from the outer surface 52 of the lens 40 propagates in a preselected direction towards a portion of the reflector 38 to reflect therefrom in a desired direction. In the preferred embodiment, the phase shifters 48 are spaced sufficiently close together such that there is substantially no effect of grating nulls and grating lobes within the region of 0 degrees over which the rays of radiation emanating from the lens 40 are scanned. However, the resultant beam 56 generated by the reflections of these rays upon the concave surface of the reflector 38 is scanned over an arc of only :10 degrees, the lens 40 and reflector 38 thus cooperating to provide an apparent demagnification of the scan angle. In spite of the limited scan capability of the antenna 32, multiple target tracking (in angle) is readily employed for aircraft 34 within the general vicinity of the flight path of the runway 36 by simply redirecting the beam 56. The system 30 is responsive to radiation of the beam 56 reflected from the aircraft 34 as well as radiation, such as that of a transponder, generated within the aircraft 34.

A base 58 connects with a frame 60 for supporting the reflector 38, the frame 60 furthermore providing stability for retaining the shape of the reflector 38 even in the presence of wind forces. The base 58 is provided with a strut 62 to which an arm 64 is pivotally connected by a pivot 66. The arm 64 is physically connected, as is indicated by dashed lines 68 and 70, to the lens 40 and the horn 42 for supporting them in a preselected relation to the reflector 38; this preselected relation may be altered by means of a motor 72 which is energized by conventional means, not shown, for pivoting the arm 64 about the strut 62 to adjust the distance between the lens 40 and the reflector 38. It is noted, in this connection, that the pivoting of the arm 64 about the strut 62 conveniently provides for a zoom effect in which the width of the beam 56 and its active aperture 46 may be made to vary.

The horn 42 is preferably constructed in the manner of a monopulse feed and may comprise four waveguide sections which connect with an electronic unit 74 via set of four waveguides represented in the figure by lines 76. Thus, each line 76 carries a portion of the signal transmitted or received by horn 42 and, with respect to received signals, a difference in phase between the signal on one of the lines 76 and the signal on another of the lines 76 provides information as to the elevation and azimuthal angular offset of the aircraft 34 from the center of the beam 56. The elevation and azimuthal angular coordinates of the direction of the beam 56 are known by virtue of the phase shift signals on lines 54.

The electronic unit 74 comprises a waveguide comparator 78, a transmitter 80, a receiver 82, a duplexer 84 inserted in the sum channel of the waveguide comparator 78 for connecting the waveguide comparator 78 to the transmitter 80 and the receiver 82, a signal processor 85, a computer 86, a beam steering unit 88, a display 90, a console 92 by which an operator may control the entry of data displayed on the display and processed by the computer 86, and a system timing unit 94 which transmits timing signals along lines 96, 98, 100 and 102 for timing and synchronizing the operations of, respectively, the beam steering unit 88, the display 90, the computer 86 and the signal processor 85.

The waveguide comparator 78 and horn 42 are typically constructed as a single unit which functions as a multimode monopulse feed and comparator such as that disclosed by Peter Hannon in the Transactions of the Institute of Radio Engineers Professional Group on Antennas and Propagation, September, 1961, wherein higher order modes of radiation propagate in a horn such as the horn 42. As is well known, such a structure provides for a substantially equal spread in both the sum and difference directivity patterns. The comparator 78 comprises, for example, well-known hybrid mixers by which the lines 76 are interconnected for performing the arithmetic operations of obtainingthe difference between the signals on the lines 76 to provide the elevation difference signal on line 104 and the azimuth difference signal on line 106, while the sum of the signals on all four of the lines 76 provides the aforementioned sum channel signal on line 108. The duplexer 84 which is of conventional design permits propagation of the signal from the transmitter 80 along lines 110 and 108 to the waveguide comparator 78 and thence to the horn 42 while isolating the receiver 82 from this signal; upon reception, the duplexer 84 directs a signal appearing on line 108 to the receiver 82. The receiver 82 may be a conventional three-channel receiver which provides elevation and azimuth angle error signals via line 112 to the computer 86 which may then utilize this data to reposition the beam 56 for tracking the aircraft 34. Where several aircraft 34 appear within the beam 56, range gating signals may be applied along line 113 to facilitate tracking (in range) of the individual aircraft. In addition, the signal received on the sum channel is further processed by the signal processor 85 which may comprise pulse compression circuitry for discrimination between aircraft that are closely spaced in range, or, the signal processor 85 may utilize correlation techniques in which a low powered duplicate of the transmitted signal is provided as a reference along line 114 against which a correlation is made to provide discrimination between aircraft which are closely positioned in range. The range which is determined by the temporal relationship of the received signal and the timing signal on line 102 is transmitted via line 116 to the computer 86. Steering of the beam 56 is provided by angle commands generated by the computer 86 and transmitted via line 118 to the beam steering unit 88. The beam steering unit 88, in response to these angle commands, generates the set of aforementioned phase shifter command signals which are applied via the lines 54 to the phase shifters 48.

It is frequently desirable to utilize an area surveillance radar 120 having an antenna 122 and feed 124 which rotate about a base 126 to provide the position coordinates of an aircraft, namely, range, elevation, azimuth and their derivatives along line 128. A wellknown coordinate converter 130 converts these values of the position coordinates to a set of values corresponding to the position of the antenna 32. These converted values are then transmitted along line 132 to the console 92 for entry along line 134 into the display 90 for displaying the positions of aircraft in the vicinity of the runway 36, and for entry along line 136 into the computer 86 to initiate tracking of'one of such aircraft as selected by the console 92.

Referring now to FIG. 2, there is shown an alternative embodiment of the antenna of the invention comprising a horn 138, a lens 140 comprising a plurality of phase shifters 142 for directing radiation emanating from the horn 138, and a lens 144 made from a ceramic or plastic material or, alternatively, by parallel spaced waveguides 146 indicated diagrammatically for collimating the rays of radiation traversing the lens 140. The lens 144 is convex so that rays of radiation incident on the central portion of the lens 144 are retarded rela tive to rays incident near the periphery of the lens 144 to accomplish the aforesaid collimation. It should be noted that the lens 144 and the lens cooperate together in the same manner as do the reflector 38 and the lens 40 of FIG. 1.

Referring now to FIG. 3, there is shown still a further embodiment of the antenna of the invention in which the lens 40 of FIG. 1 has been replaced with a subreflector 148 comprising an array of phase shifters 150 for directing radiation incident thereupon from a horn 152 to a reflector 154, the subreflector 148 accomplishing a steering of the rays of radiation in a manner analogous to that of the lens 40 of FIG. 1. In both FIGS. 2 and 3, the elements of the antenna are supported and positioned by support structures well known to the art and not seen in the figures. It is also understood that the reflector 154 of FIG. 3 may alternatively be replaced by a lens similar to the lens 144 of FIG. 2.

As has been mentioned hereinbefore, a basic feature of the invention is the illumination of the reflector 38 i of FIG. 1 in such a manner that the active apertures 46 retain their shape and uniformity of illumination irrespectively of their location on the antenna 38. This is accomplished by selecting the appropriate curvature to The reflector 38 is substantially larger than the lens 40 and is placed within the near field of the lens 40, that is, at a sufficiently close distance such that the mathematics of Fresnel optics are: employed in calculating the beam of radiation 56 which results from the coaction of the lens 40 with the reflector 38 and acting substantially as a single focusing ellement comprised of two subelements, namely, the lens 40 and the reflector 38. This is to be distinguished from prior art systems in which a plurality of microwave lenses or other focusing elements are arranged to accomplish a desired focusing or directing of a beam of radiation. In the prior art systems these focusing elements are at a substantial spacing, within the Fraunhofer or far field region, while the elements of the present focusing system are within the Fresnel region or near field.

The lens 40 is provided with a curved surface to minimize the amount of radiation which would be directed at glancing angles from the phase shifters 48 towards the reflector 38. This minimizes the effects of mutual coupling between the various phase shifters 48 and provides for increased power to the radiated radiation since this radiation can be radiated in a direction substantially normal to the face of the phase shifter 48 thereby substantially avoiding the effect of reduced gain in the directivity pattern of each of the phase shifters 48 at a glancing angle. The curvature of the lens 40 also facilitates capturing the radiation emanating from the horn 42, this radiation emanating in substantially radial directions from the horn 42 with a curved generally spherical wavefront, such a wavefront being most readily received by phase shifters arranged along a concave surface as are the phase shifters 48 of the lens 40. In the preferred embodiment, the spacing between the lens 40 and the horn 42 is preferably in the far field of the horn 42 (at a distance somewhat greater than 2D /A, wherein D is the diagonal of the aperture of the horn42 and )t is the wavelength of the radiated radiation).

In selecting a curvature for the reflector 38, it is desirable to utilize a curved surface which may be described by a simple mathematical expression, such as a hyperbola of revolution, or hyperboloid, wherein an entire family of curved surfaces can be described simply by two parameters, such as the eccentricity and the axial distance between a focus and the hyperboloid. By simply varying these parameters, as well as the relative positions between the reflector 38 and the lens 40, an iterative routine may be employed by a computer to provide a mapping of points on the lens 40 to the corresponding points within the active aperture 46, for example, points along a vertical line and points along a horizontal line, so that the general configuration of the active aperture 46 can be seen without actually fabricating the antenna 32. This mapping of the points on the lens 40 to the active aperture 46 upon the reflector 38 will now be described.

Referring now to FIG. 4, there are seen construction lines utilized in the mapping procedure. The first step is to determine the size, position and location of the array of phase shifters comprising the lens 40 of FIG. 1, here indicated by a rectangle 156. The reflector 38 is here indicated by a sectional view of a hyperboloid 158. In this configuration, as in FIG. 1, the rectangle 156 is offset from the hyperboloid 158 so that there is no blockage by the rectangle 156 of beams of radiation reflected from the hyperboloid 158. First, a central beam 160 and two extreme beams 162 and 164 are established representing the beams of radiation in, respectively, an undeflected position, at an azimuthal angle of therefrom, and at an azimuthal angle of minus 10 therefrom. The procedure here is demonstrated for an azimuthal plane, while it is understood that the same procedure is repeated for an elevation plane. The beam 160 is bounded by an upper ray 166 and a lower ray 168, the beam 162 is bounded by an upper ray 170 and a lower ray 172 while the beam 164 is bounded by an upper ray 174 and a lower ray 176. The rays 170 and 172 are spaced apart a distance equal to the spacing between the rays 166 and 168 as well as the spacing between the rays 174 and 176. The beams 160, 162 and 164 are presumed to be incident from external sources upon the hyperboloid 158, with radiation travelling in a direction indicated by the arrows on the rays 166, 170 and 174. The beam 162 illuminates an active aperture 178 similar to the active aperture 46 of FIG. 1, and the beam 164 similarly illuminates an active aperture 180.

To determine the bounds of the rectangle 156, the ray 170 is traced towards the hyperboloid 158 whereupon it reflects back as ray 170A, and the ray 166 similarly reflects off the hyperboloid 158 as ray 166A to intersect with the ray 170A at point 182. Point 184 is a similarly found to be at the intersection of the rays 168A and'176A which represent, respectively, the reflections of the rays 168 and 176. The points 182 and 184 represent the bounds of the front surface of the array of phase shifters here represented by the rectangle 156. While the rays and 172 are essentially par allel, the reflected rays 170A and 172A are generally not parallel since, as can be seen in FIG. 4, the angles of incidence and reflection of the various rays vary with their points of interception by the hyperboloid 158. It is noted that this construction can be provided for a conic section of any eccentricity and focal length and is valid for electromagnetic radiant energy, sonic radiant energy as well as light. (For example, ellipsoids and hyperboloids have eccentricities respectively less than and greater than unity.)

The next part of the mapping procedure is to direct rays from each point of a line 186 joining the points 182 and 184 towards the hyperboloid 158 to generate the beams 160, 162 and 164 now travelling in a direction outwardly from the hyperboloid 158. The line 186 represents the front face in an azimuthal cross section of the array of phase shifters 48 comprising the lens 40 of FIG. 1. In plotting these additional rays, the points of reflection from the hyperboloid 158 will be noted.

Before continuing with a description of a ray tracing program to be utilized in obtaining the mapping, two examples of mappings will be presented in FIGS. 5 and 6, and the actual geometry utilized in the preferred embodiment will be seen in FIGS. 7A and 78.

Referring now to FIGS. 5 and 6, there are shown two mappings of the points of reflection upon the hyperboloid 158, these points of reflection being designated by the numeral 188 which are seen located within active apertures 178A and 1783, both of these apertures being distorted in these figures, by way of example, for demonstrating an improper selection of hyperboloid 158. The active apertures 178A and 1788 are shown in two dimensions, both elevation and azimuth, to demonstrate that while there may be symmetry in the elevation axis, this does not necessarily bring symmetry to the azimuthal axis. The distortion is readily seen in FIG. 6 by comparing the shape of the active apertures 178A and 1783 with the desired aperture 189 shown in dashed lines. This distortion would produce a clearly undesirable result for a monopulse tracker since it is clear that the phase center of the four quadrants 190A-D is displaced from the center of the active aperture 1788. For example, in obtaining the difference frequency for the elevation error signal of a monopulse tracker, it is evident that there would be a boresight error in the case of the active aperture 178B, and that furthermore, this error would vary with the elevation angle since the distortion of the active aperture 178B varies with the position of this aperture upon the reflecting surface of the hyperboloid 158.

Referring now to FIGS. 7A and 7B, there are shown two diagrammatic views of the antenna 32 of FIG. 1, respectively a horizontal or top view in a graph having X-Z coordinates and an elevation or side view shown in a graph having X-Y coordinates. The reflector 38 is shown diagrammatically as a sectional view of a hyperboloidal sector. The diagrammatic view of the reflector 38, and lens 40 and the horn 42 are shown superimposed upon the graphs to show the dimensions and placement of these elements as utilized in the preferred embodiment of this invention for providing the active aperture 46 of FIG. 1 which is uniformly formed invariant of its position upon the reflector 38, thereby providing the beam 56 with a directivity pattern invariant of the direction of the beam 56. The reflecting surface of the reflector 38 is described in the figure by means of an equation of the hyperboloid of which is this surface is simply a sector thereof. All dimensions shown in the figure are in inches. The coordinates X, Y and Z int the equation refer to the coordinates of the graph. The reflector 38 extends from a value of Z 43 inches to a value of Z 153 inches in the horizontal plane, and from a value of Y 62 inches to a value of Y +78 inches in the vertical plane. The lens 40 and the horn 42 share in a common axis 192 which is inclined relative to the X-axis as seen in the figure at an angle of 47.9". The end points of the front surface (facing the reflector 38) of the lens 40 are shown in the horizontal plane by the coordinate values X 60.31 inches and Z 18.52 inches for one end point while the coordinates of the'other end point are X 80.52 inches and Z 36.80 inches. The radiating aperture of the horn 42 is spaced from the back face of the lens 40 by a distance of 26 inches along the axis 192. The lens 40 is curved as shown in the auxiliary view 194 which portrays the lens 40 in diagrammatic form within a plane containing the axis 192 and perpendicular to the X-Z plane. In the auxiliary view 194, the lens 40 is seen to be curved with a radius of curvature of 65 inches, the center of curvature being positioned at the coordinates Y 0, X l 14.01 inches and Z =20.55 inches. Thus, the lens 40 has a front face and a back face, each of which has the form of a sector of a circular cylindrical surface. The vertical coordinates of the lens 40 are shown in the X-Y plane, with the upper edge of the lens 40 having a value of Y +20 inches and the lower edge of the lens 40 having a value of Y 20 inches. In the horizontal or azimuthal plane, the antenna 32 scans a beam of radiation within a 20 degree arc which is centered at an angle of 3.4 relative to the X-axis as seen in the figure. The antenna 32 scans a beam of radiation in the vertical or elevation plane through an arc of of which approximately 6 is below the horizontal plane while approximately 9 is above the horizontal plane.

The desired configuration of the antenna elements as presented by FIGS. 7A and 7B has been obtained, as has been mentioned hereinbefore, by a ray tracing program utilizing a computer. Continuing with the ray tracing program, the coordinates of the points of reflection along the hyperboloid 158 of FIG. 4 are readily obtained with the aid of the equation of the hyperboloid. For example, in constructing the rays of the beam 162, the rays emanating from the lens as represented by the rectangle 156 are constructed by an iterative procedure (following the Newton successive approximation procedure) in which a ray is drawn from a point on the line 186 in a direction approximately parallel to the ray 170A to a point of intersection on the hyperboloid 158, and then a second ray is traced from that point of intersection in a direction parallel to the ray 170. The angle of incidence and reflection of these two rays is then compared after which the two rays are redrawn to a slightly offset position of intersection upon the hyperboloid 158 whereupon the angles of incidence and refraction are again compared, this procedure being repeated until these two angles are substantially equal. Then another pair of rays, one approximately parallel to the ray 170A and the other parallel to the ray 170, are traced from another point on line 186 to a separate point of intersection on the hyperboloid 158 and the iterative procedure is again repeated for adjusting the point of intersection on the hyperboloid 158 to a position wherein the angle of incidence equals the angle of reflection. The result is the plot of these points of intersection seen hereinbefore as the points 188 in FIGS. 5 or 6. The computer routine then continues with a repeat of this ray tracing program but for a hyperboloid 158 having a different eccentricity and/or focal length. Successive hyperboloids 158 of differing parameter values are then utilized in the computer program until an optimum set of values, those shown in FIGS. 7A and 7B, are obtained.

It should be noted in this respect that the curvature of the lens 40 has not yet been employed in the ray tracing program since a cylindrical lens with zero curvature in azimuth is utilized. However, essentially the same procedure of mapping is employed in the elevation plane by employing a mathematical expression describing the curved surface to be utilized in the lens 40 which is inserted into the ray tracing program.

Referring now to FIGS. 1 and 8, the beam steering signals applied to the phase shifters 48 along lines 54 from the beam steering unit 88 are computed by the beam steering unit 88 in accordance with a program derived from a ray tracing procedure presented in FIG. 8. The reflector 38, the lens 40 and the horn 42 of FIG. 1 are seen diagrammatically in FIG. 8. The phase shift to be introduced by a phase shifter 48 to a ray of radiation travelling from the horn 42 through the phase shifter 48 to the reflector 38 and then to the aircraft 34 depends on the angle of the beam 56, or equivalently, the angle of a wavefront indicated diagrammatically and identified by the numeral 196 in FIG. 8. A second wavefront 198, shown as a dashed line in the figure, propagates in a direction different from that of the wavefront 196.

In FIG. 8, two beams of radiation are shown, the first beam having the wavefront 196 and comprising rays 200,201 and 202, and the second beam having wavefront 198 and comprising rays 203, 204 and 205. Each of these six rays are shown reflecting off the reflector 38 as rays, correspondingly identified by numerals 200A-205A, which pass through phase shifters 48 of the lens 40 to the horn 42. With respect to the three rays 200-202, each of these rays are in phase with each other at the wavefront 196. However, the electrical length, in terms of wavelengths, of the paths of ray 200 plus ray 200A differs from that of ray 201 or 202 plus respectively ray 201A or 202A. The phase difference in the paths of radiant energy from the horn 42 to the wavefront 196 is compensated by the phase shifters 48 which provide additional phase shift to each ray to equalize the phase of the respective rays at the wavefront 196. The amount of phase compensation required by each phase shifter 48 to accomplish the phase equalization is readily computed by a computer programmed for a ray tracing routine based on the positions and orientations of the elements of the antenna 32 and the wavefront 196. These computed values of phase shift are the identical values required to generate a beam of radiation having the wavefront 196.

In the same manner, a set of phase shift values are computed with respect to the wavefront 198. The phase shifters 48 provide these values of phase shift modulo 360. The phase shift for other beam directions is further provided by the computer routine simply by rotating the wavefront 196 about the point 208 to other orientations (such as that of wavefront 198) and repeating the computation.

The above routine is repeated for a sufficient number of orientations of the wavefront 196 to permit the plotting of a graph of phase shift of each phase shifter 48 versus beam direction. Such a graph is generated for each phase shifter 48 as a function of elevation at zero azimuth, and a second one of these graphs is generated for each phase shifter 48 as a function of azimuth at zero elevation. This pair of graphs for each phase shifter 48 is closely approximated by a polynomial in the form of a power series, namely,

in which 6 represents the azimuthal angle while 4) represents the elevation angle and a is the total contribution of phase shift provided by the k" phase shifter 48, there being 824 phase shifters 48 in the preferred embodiment of the antenna 32. The symbols C C represent a set of five constants for each of the k phase shifters 48. As seen by the above equation, both the elevation and the azimuthal contributions are treated separately and interaction terms between them do not appear.

- It has been found that the approximation for phase shift represented by the above equation does, in fact, provide a reasonably accurate prediction of the amount of phase shift a which must be produced by the kth phase shifter such that with each of the phase shifters providing the required phase shift contribution as indicated above by Equation 1, the beam 56 of FIG. 1 is steered to elevation and azimuth angles approximating the values of and (b utilized in Equation 1.

To determine the exact angular deviation of the beam 56 from that predicted by the aforesaid equation, a computer simulation of the antenna 32 is conducted in which the contributions of all of the phase shifters are summed together to compute the resulting beam 56 which is generated by the contributions of all the phase shifters 48, each of which is providing the phase shift designated for that phase shifter in accordance with Equation 1. The elevation azimuthal components of the direction of the beam 56 as computed by this computer simulation are then compared with the elevation and azimuthal components, namely, (1) and 0, which were substituted in Equation 1 to determine the correction which must be applied to beam steering commands. The necessary correction is computed for various directions of the beam 56, and it has been found that these corrections can be expressed by an empirical equation that is evaluated within the beam steering unit 88. The correction to the beam steering command given on the lines 54 is accomplished by means of the beam steering unit 88 by converting each of the angle signals on line 118 to a slightly different angle by adding in the necessary angular corrections as computed within the beam steering unit 88 (as will be described below) so that the beam steering commands provided on the lines 54 are such as to steer the beam 56 in the desired direction.

Referring now to FIGS. 9, and 11, there is shown a detailed block diagram of the beam steering unit 88 of FIG. 1 including the interconnections with the driver circuits for the phase shifters 48 of FIG. 1. FIG. 9 shows the beam steering unit 88, while FIG. 10 shows the driver circuits 250 for establishing the magnetic flux in the ferrite material of the phase shifters 48, one such driver circuit 250 being collocated with each one of the phase shifters 48. The phase shifts of each of the phase shifters 48 of the lens 40 are set to an appropriate value in response to the drive signals of the driver circuits 250, these drive signals being seen in the timing diagram of FIG. 11.

Referring now specifically to FIG. 9, the beam steering unit 88 is shown having an angle command received on line 1 18 as well as timing signals received on line 96, both of these signals having been previously mentioned with reference to FIG. 1. In addition, there is seen the set of output lines 54 from the beam steering unit 88, which as has been seen in FIG. 1, connect with respective ones of the phase shifters 48. With respect to the timing signal on line 96, this signal comprises various clock pulses and synchronizing pulses which are well known to digital equipment and are applied, for example, to shift registers, control logic, pulse generators and arithmetic units; such utilization of timing signals is well known and is, accordingly, shown in FIG. 9 symbolically with the line 96 seen terminating at the dashed line enclosing the beam steering unit 88 without showing the connections to the individual components of the beam steering unit 88.

The beam steering unit 88 comprises a compensator 252 which alters each beam steering angle appearing on line 118 to compensate for the angular offset which was described hereinbefore with reference to the ray tracing of FIG. 8 and the values of phase shift as given by Equation 1. The revised angle appears on line 254. The compensator 252 comprises an angle sense unit 256 responsive to the elevation and azimuthal angles, a memory unit 258 and an arithmetic unit 260, the arithmetic unit 260 adding in a correction term from the memory unit 258 to the angle on line 118 to give the revised angle on line 254. The appropriate correction term is obtained from the memory 258 by means of an address supplied along line 262 in response to a computation by the angle sense unit 256 based on a formula utilizing the magnitude of the elevation and azimuthal angles.

The requisite phase shift to be applied by each of the phase shifters 48 in FIG. 1 to radiation provided by the horn 42 to steer the beam 56 with the desired elevation and azimuthal angles is obtained by means of a computation unit 264 which implements the calculations of Equation 1, namely, the multiplication of the elevation and azimuthal angles by the respective constants C and C the squaring of the elevation azimuthal angles and multiplication of the squared values respectively by the constants C and C and the summation of these terms with the constant C The appropriate values of the elevation and azimuthal angles, respectively dz and 0, are provided along line 254, and the requisite values of phase as computed by the computation unit 264 appear as three-bit binary numbers on the lines 266A-C with the individual bits appearing on respective ones of the lines 266A-C. A memory unit 268 stores separate sets of the constants C -C one of these sets for each of the phase shifters 48 of FIG. 1. In the preferred embodiment, corresponding to the 824 phase shifters 48, there are 824 sets of the constants C -C in storage requiring 44 bits of memory for each phase shifter 48. Thus, the computation unit 264 must repeat the computations 824 times, and in each of the computations utilizing the set of constants C -C appropriate to the particular phase shifter 48. Coordination of these computations, as well as the addressing of the appropriate sets of constants in the memory unit 268, is provided bya control logic unit 270 seen interconnecting with the phase computation unit 264 and the memory unit 268, respectively, along lines 272 and 274. A control logic unit, such as the control logic unit 270, as well as the memory unit 268 and the phase computation unit 264, is readily constructed using well-known techniques of digital computation and need not be described further.

Since all rays of the beam 56 of FIG. 1 are to be simultaneously steered in a given direction, each of the phase shifters 48 is to receive its phase shift drive signal along line 54 at the same time. Accordingly, the computed values of phase shift appearing serially for each of the phase shifters 48 along the lines 266A-C must be temporarily stored until the values for all of the phase shifters 48 have been computed whereupon these values of phase shift can be simultaneously transmitted along the lines 54 to each of the phase shifters 48. This temporary storage is provided by three shift registers 276A-C, each of which contains a number of cells, or bit storage, equal to the number of phase shifters 48 comprising the lens 40 of FIG.'1; thus, each of the shift registers 276A-C has 824 cells in the preferred embodiment of the invention. A few of these cells are shown by way of example in FIG. 9 and are numbered 1, 2, 823, 824. The cells numbered with the numeral 1 store the bits of the binary number representing the phase shift command for a phase shifter 48 which is arbitrarily designated phase shifter No. 1. Similarly, the cells designated No. 2 of the shift registers 276A-C store the bits of the binary number representing the phase shift required for the No. 2 phase shifter. Since each of the shift registers 276A-C stores only one bit of the three-bit binary number appearing on lines 266A-C, the bit stored by shift register 276A corresponds to a phase angle of 45 while the bits stored by shift registers 276B-C correspond respectively to phase angles of 90 and 180.

Each of the shift registers 276A-C has parallel output lines for controlling multiplexer selector switches 278, there being one multiplexing switch 278 for each of the 824 phase shifters, with each of the multiplexer switches 278 having three inport ports labelled A, B and C for receiving the respective bits of the binary numbers from the cells of the respective shift registers 276A-C. the No. 1 cells of the shift registers 276A-C connect with the multiplexing switch 278 labelled MUX No. 1, and the cells No. 2 of the shift registers 276A-C connect with the multiplexer switch 278 labelled MUX No. 2, with similar interconnections being made with the other multiplexing switches 278. The multiplexing switches 278 are well known and each is the digital equivalent of a single-pole multiple-throw mechanical switch in which the single output of the multiplexer switch 278 on line 280 is connected to one of the lines 282, the particular interconnection of a line 282 with the line 280 being selected in accordance with the binary number appearing at the terminals A, B and C of the multiplexer switch 278.

"As has been mentioned hereinbefore with reference to establishing the appropriate magnetization of the ferrite material in each of the phase shifters of the lens 40 of FIG. 1, a voltage pulse having a predetermined time duration is applied to a winding surrounding the ferrite material such that the magnetizing flux which is proportional to the integral of the voltage of the pulse has the appropriate value to provide the desired phase shift. The requisite pulse duration to establish phase shifts of 45, 315, has been established experimentally for the particular ferrite material utilized in the phase shifters, and a pulse generator 284 is provided to generate voltage pulses along the lines 282 having the requisite pulse width. As seen in the figure, the pulse width on the line 282 providing a 45-degree phase shift is relatively narrow, no pulse being seen on the line 282 representing 0, the pulse for a 90-degree phase shift being approximately double the pulse which provides the 45-degree phase shift, and the longest pulse duration being that utilized for providing the 3 15- degree phase shift. The use of the pulse generator 284 in providing a set of pulses on lines. 282 of any predetermined pulse width in cooperation with the multiplexer switches 278 forselecting these pulses permits compensation for nonlinearities within the phase shifters 48, thereby providing precise control of the phase shift. There are a total of eight lines 282 for providing any amount of phase shift in the aforesaid manner, namely, modulo 360, in increments of 45. The pulse generator 284 also provides a mode signal on line 285 which is utilized in the setting and resetting of the phase shifters in a manner to be described with reference to FIGS. 10 and 11. Each line 280 containing a selected strobe signal is coupled via an OR circuit 286, to be described hereinafter, to a line 287. Each line 287 and the line 285 carrying the mode signal are combined in separate cables for each of the phase shifters, each cable being indicated by the line 54 seen here in FIG. 9, as well as in FIG. 1.

Referring now to FIG. 10 there is shown a schematic diagram of the driver circuit 250 and its interconnection with the coils 288 and 290 of the phase shifter 48. The driver circuit 250 comprises digital inverters 292, 294, 296 and 298 (converting a logical one to a logical zero and vice versa), NAND gates 3 and 302 and a pair of emitter follower circuits 304 and 306, each of which comprises transistors 308 and 310, diodes 312 and resistors 314 and 316. The emitter follower circuit 304 energizes the coil 290 for setting the phase shifter 48 to a specific phase shift, and the emitter follower circuit 306 energizes the coil 288 for resetting the ferrite material of the phase shifter 48 to a known flux reference state. There is a driver circuit 250 for each of the 824 phase shifters 48, each of the driver circuits 250 being identical and having the circuit shown in FIG. 10.

In operation the driver circuit 250 receives digital pulse signals on the lines 285 and 287, inverts these signals by digital inverters 292 and 294 and then applies the inverted signals to the NAND gate 300. In addition, the signal on line 285 is also applied to NAND gate 302 along with the inverted form of the signal on line 287. The signals at the outputs of the NAND gates 300 and 302 are then further inverted by the digital inverters 296 and 298 applied to the emitter followers 304 and' 306. The emitter followers 304 and 306 substantially retain the waveforms of signals appearing at the outputs of the digital inverters 296 and 298 and amplify the power in these signals to a suitable level for driving the coils 288and 290. The coil 200 is serially connected with a resistor 318 in the collector circuit of transistors 308 and 310 between their collector terminals and a power supply 320. The resistor 318 and 3 capacitor 322 serve as a filter for isolating each of the coils 288 and 290 from each other as well as to attenuate any noise from the power supply 320. The coil 288 is similarly connected with a resistor 318 in the collector circuit of the emitter follower 306 between the collector terminals of the transistor 308 and 310 and the power supply 320. The resistors 314 and 316 are selected in a well-known manner for providing a suitable bias to the transistors 308 and 310. The diode 312 prevents the occurrence of an excessive negative voltage overshoot to insure proper functioning of the circuit.

' The signals appearing on the lines 285 and 287 are shown in the timing diagram of FIG. 11. The pulse waveforms of lines 282 seen in FIG. 9 are seen also in FIG. 11, three of these pulse waveforms being identified in both figures by the numerals 324, 326 and 328. They represent a portion of the strobe signal on line 280 or line 287 of FIG. 10, with the pulse waveform 324being of relatively short duration to provide the appropriate flux for a phase shift of 45 while the pulse waveforms 326 and 328 provide sufiicientflux for respectively 90 and 135 of phase shift. In FIG. 11 the pulse waveforms 324, 326 and 328 are seen to be negative going pulses having a voltage swing of typically 5 volts, but which after three inversions by means of the digital inverters 294 and 296 and the NAND gate 300 appear as a positive going pulse at the base terminal of the transistor 308. The time scale utilized in the preferred embodiment is indicated in the graph of FIG. 1 1, and it is seen that the strobe signal on line 287 has a voltage of zero volts during the first 50 microseconds and then changes to a value of 5 volts. The strobe signal reverts to the value of zero volts during the duration of a flux drive signal as is represented by the pulse waveform 324. It is noted that the trailing edge or termination of each of the pulse waveforms 324, 326 and 328 occur at 90.625 microseconds, but that the leading edges of these pulse waveforms occur at different times depending on the pulse widths. Since the phase shifters 48 are of the latching type, no further flux drive signals are transmitted to the phase shifters 48 until it is desired to redirect the beam 56 of FIG. 1.

The mode signal on line 285 is also seen in FIG. 11. It assumes a value of 5 volts for a duration of 55 microseconds and then assumes a value of zero volts for the duration of the period. During the first fifty microseconds when the strobe signal is seen having a low voltage of zero volts and the mode signal is seen having a high voltage of 5 volts, no signal appears at the output of the emitter follower 304, but a resetting signal appears at the output of the emitter follower 306. This is readily seen by tracing the logic path through the inverters 292, 294, 296 and 298 and the NAND gates 300 and 302. After a time of 55 microseconds when the mode voltage drops to the low value of zero, the output of the NAND gate 302 remains high so that no resetting signal can appear at the output of the emitter follower circuit 306. And furthermore, since the inverted mode voltage which is applied to the NAND gate 300 by the inverter 292 now has a high value, the NAND gate 300 is enabled to pass the inverted strobe signal voltage of inverter 294 whenever the inverted strobe signal voltage has a high value; this high value of inverted strobe voltage is attained during the duration of the pulse waveforms 324, 326 and 328, at which time the emitter follower circuit 304 is activated to magnetize the ferrite material of phase shifter 48 to provide the desired phase shift. In this way it is seen that the mode signal on line 285 controls the times of setting and resetting the phase shifter 48 while the strobe signal on line 287 provides the amount of flux required to produce a desired phase shift.

As a practical matter in the construction of the antenna 32 of FIG. 1, the lens 40 and horn 42 are enclosed with a covering, not shown in the figure but having the form of a miniature radome, which is transparent to the radiation transmitted by the antenna 32 and which protects the lens 40 and horn 42 from the weather. Due to this covering as well as the structure of the lens 40 itself, the lens 40 experiences a rise in temperature provided by heat dissipated therein from both the passage of the radiation through the phase shifters 48 as well as electrical currents in the driver circuits 250 of FIG. 10. As is well known, the electrical characteristics of ferrite materials such as that employed in the phase shifters 48 vary with temperature with the result that, in order to provide the antenna 32 with a truly accurate beam steering capability, it is desirable to provide a compensation for this thermally induced variation in the electrical characteristics. This heating and compensation will now be further described with reference to FIGS. 12 and 9.

Referring now to FIG. 12, there is shown in diagrammatic form a front view of the lens 40 of FIG. 1 with the various phase shifters 48 arranged in vertical columns (slightly offset from each other for improved reduction of grating lobes and grating nulls). The vertical columns in the central portion of the array of phase shifters extend from the bottom of the lens 40 to the top of the lens 40, while those columns at the edges of the array are somewhat shorter. The lens 40 is seen divided up into the thennal zones wherein the zone at the bottom experiences a temperature rise above ambient of 3.56, the lower middle zone experiences a temperature rise of 6-8, the upper middle zone experiences a temperature rise of 8-l 0, and the top zone experiences a temperature rise of l0l2.

Referring now to FIGS. 9 and 12, the compensation for the thermally induced variations in the electrical characteristics of the phase shifters 48 is accomplished by increasing the flux drive to the ferrite material. Accordingly, additional phase shifter driver signals are provided by the pulse generator 284 along lines 230, these compensation drive signals having a rectangular pulse waveform which pulse widths ranging from a value of zero (no temperature compensation) for the warmest phase shifters 48 of FIG. 12 to a pulse width of approximately 1.1 microseconds to the coolest phase shifters 48 of FIG. 12. Also, as is indicated in FIG. 12, the compensation drive signals on lines 230 having pulse widths of approximately 0.3 and 0.6 microseconds are applied to the phase shifters 48 respectively in the upper and lower middle thermal zones. The compensation drive signals are coupled from lines 230 to the driver circuits 250 of FIG. 10 via lines 232 and OR circuits 286 of FIG. 9 to the lines 287 and thence along the lines 287 to the driver circuits 250. The driver circuits 250 respond to the compensation drive signals on lines 287 in the same manner as described above with reference to the strobe signals on the lines 287. As seen in the timing diagram of FIG. 11, the compensation drive signals (seen in the graph labeled TEMP.

COMP") are conveniently applied immediately after the termination of any one of the pulse waveforms 324, 326 or 328 of the strobe signal.

Referring now to FIG. 13, there is seen a timing diagram for the system of FIG. 1. The timing diagram is composed of a repetitive sequence of alternating intervals labeled A and B, the former being of 90 microseconds duration and the latter varying from 660 microseconds to 1,000 microseconds. During interval A the computer 86 provides angle data for directing the beam 56, and the beam steering unit 88 adjusts the phase shifts of the phase shifter 48 to provide the desired beam direction. During the interval B the system 30 communicates with the aircraft 34 by transmitting and receiving radiant energy signals between the antenna 32 and the aircraft 34. This communication with the aircraft 34 can be improved by utilizing a transponder 234, seen located within the aircraft 34 in FIG. 1, the transponder 234 serving to identify the aircraft as well as supplying supplementary data such as the altitude of the aircraft 34. The computer 86, during interval B, computes the next direction of the beam 56 based on trajectory data of the aircraft 34 obtained via the antenna 32 as well as from the area surveillance radar 120 and data entries made at the console 92.

It is understood that the above-described embodiments of the invention are illustrative only and that modifications thereof will occur to those skilled in the art. Accordingly, it is desired that this invention is not to be limited to the embodiments disclosed herein but is to be limited only as defined by the appended claims.

We claim:

1. A system for obtaining data relative to a source of radiation, said system comprising:

first means for altering the direction of a wavefront of radiation of said source incident upon said first means by altering the phase of one ray of said radiation relative to another ray of said radiation, said first means comprising regions through which said rays of radiation propagate, the phase length of one of said regions being variable with respect to the phase length of another of said regions to permit a varying of said direction;

second means for altering the direction of one ray of radiation incident thereupon relative to another ray of radiation incident thereupon, said second means being positioned from said first means such that said rays of radiation propagate from one of said means to the other of said means, said second means having a curved surface from the class of surfaces consisting of hyperboloids and ellipsoids, an arc of said curved surface lying in a plane containing a plurality of said wavefront directions altered by said first means, the amount of said altering of direction by said second means being selected in accordance with the amount of said altering of said phase by said first means in a manner which retains a uniformly formed radiating aperture independently of said direction; and

third means coupled to said first means and said second means for extracting data relative to said source from said radiation.

2. The system according to claim 1 further comprising fourth means coupled to said first means for varying the phase length of one of said regions independently of the phase length of another of said regions thereby accomplishing a scanning of radiation, said second means being sufficiently curved to reduce the angle of scanning of a radiation which propagates from said first means to said second means.

3. A system for obtaining data relative to a source of radiation, said system comprising:

first means for altering the direction of a wavefront of radiation of said source incident upon said first means by altering the phase of one ray of said radiation relative to another ray of radiation, said first means comprising regions through which said rays of radiation propagate, the phase length of one of said regions being variable with respect to the phase length of another of said regions to permit a varying of said direction; second means for altering the direction of one ray of radiation incident thereupon relative to another ray of radiation incident thereupon, said second means being positioned from said first means such that said rays of radiation propagate from one of said means to the other of said means, the amount of said altering of direction by said second means being selected in accordance with the amount of said altering of said phase by said first means in a manner which retains a uniformly formed radiating aperture independently of said direction, said second means comprising a surface having the form of a conic section of revolution about an axis, said axis of revolution coinciding with the axis of the conic section; third means coupled to said first means and said second means for extracting data relative to said source from said radiation, said data being trajectory data of said source with respect to a movement of said source relative to said system; and fourth means coupled to said first means for varying the phase length of one of said regions independently of the phase length of another of said regions, said fourth means being further coupled to said third means, said third means utilizing said trajectory data for adjusting said phase lengths of said regions to provide a receiving beam to intercept a future position of said source to receive radiation therefrom. 4. The system according to claim 3 further comprising' fifth means coupled to said first and said second means for transmitting radiation towards said source.

5. The system according to claim 43 wherein said fifth means is coupled to said third means, said third means correlating received radiation signals with transmitted radiation signals.

6. A focusing system comprising: first means for altering the direction of a wavefront of radiation incident thereupon by altering the phase of one ray of said radiation relative to and independently of the phase of another ray of said radiation; and

second means positioned from said first means such that said rays of radiation propagate from one of said means to the other of said means, said second means altering the direction of one ray of radiation relative to another ray of radiation incident thereupon, said second means having a curved surface from the class of surfaces consisting of hyperboloids and ellipsoids, an arc of said curved surface lying in a plane containing a plurality of said wavefront directions altered by said first means, a central axis of said first means being angled with respect to an axis of said second means containing a focal point of said curved surface of said second means, the amount of said altering of direction by said second means being selected in accordance with the amount of said altering of said phase by said first means to generate a beam of radiation having a substantially uniform directivity pattern independently of the direction of propagation of said beam of radiation.

7. The focusing system according to claim 6 wherein said first means comprises phase shifting elements responsive to phase shifter control signals while providing electronically selectable phase shifts, said focusing system further comprising means responsive to a beam steering command signal for generating said phase shifter control signals thereby accomplishing a scanning of radiation, said second means being sufficiently curved to reduce the angle of scanning of a radiation which propagates from said first means to said second means, said signal generating means comprising means for computing the values of phase shift to be selected for each of said phase shifters to direct said rays of radiation in the direction corresponding to said beam steering command.

8. The focusing system according to claim 6 wherein said first means comprises phase shifting elements responsive to phase shifter control signals for providing electronically selectable phase shifts, said focusing system further comprising means responsive to a beam steering command signal for generating said phase shifter control signals thereby accomplishing a scanning of radiation, said second means being sufficiently curved to reduce the angle of scanning of a radiation which propagates from said first means to said second means, said signal generating means comprising means providing a set of pulse signals each of which is adapted to obtain a predetermined phase shift of said phase shifters, and means responsive to said values of phase shift computed by said computing means for coupling specific ones of said pulse signals to individual ones of said phase shifters.

9. In combination:

means for reflecting radiant energy;

a source of radiant energy; and

means for focusing rays of said radiant energy of said source and directing said focused rays in a direction toward said reflecting means, said focusing means comprising regions through which said rays of radiant energy propagate, the phase length of one of said regions being variable with respect to the phase length of another of said regions to permit a varying of said direction, said reflecting means having a surface curved from the class of surfaces consisting of hyperboloids and ellipsoids for intercepting said rays from said focusing means in a manner which retains a uniformly formed radiating aperture independently of said direction, an arc of said curved surface of said reflecting means lying in a plane containing a plurality of said ray directions altered by said first means.

10. The combination according to claim 9 wherein said regions of said focusing means comprise phase shifters providing electronically selectable phase shifts thereby accomplishing a scanning of said rays of radiant energy, said reflecting means being sufiiciently curved to reduce the angle of scanning of a radiation which propagates from said focusing means to said reflecting means, said focusing means further comprising means responsive to a beam steering command signal for generating phase shifter control signals for selecting the phase of said phase shifters.

11. The combination according to claim 9 wherein said regions of said focusing means comprise phase shifters providing electronically selectable phase shifts thereby accomplishing a scanning of said rays of said radiant energy, said reflecting means being sufficiently curved to reduce the angle of scanning of a radiation which propagates from said focusing means to said reflecting means, said focusing means further comprising means responsive to a beam steering command signal for generating phase shifter control signals for selecting the phase of said phase shifters, said signal generating means comprising means for computing the values of phase shift to be selected for each of said phase shifters to direct said rays of radiant energy in the direction corresponding to said beam steering command.

12. The combination according to claim 9 wherein said regions of said focusing means comprise phase shifters providing electronically selectable phase shifts thereby accomplishing a scanning of said rays of radiant energy, said reflecting means being sufiiciently curved to reduce the angle of scanning of the radiation which propagates from said focusing means to said reflecting means, said focusing means further comprising means responsive to a beam steering command signal for generating phase shifter control signals for selecting the phases of said phase shifters, said signal generating means comprising means for computing the values of phase shifts to be selected for each of said phase shifters to direct said rays of radiant energy in the direction corresponding to said beam steering command, said signal generating means further comprising means providing a set of pulse signals each of which is adapted to select a predetermined phase shift of said phase shifters, and means responsive to said values of phase shift computed by said computing means for coupling specific ones of said pulse signals to individual ones of said phase shifters.

13. In combination:

means for reflecting radiant energy;

a source of radiant energy;

means for focusing rays of said radiant energy of said source and directing said focused rays in a direction towards said reflecting means, said focusing means comprising regions through which said rays of radiant energy propagate, the phase length of one of said regions being variable with respect to the phase length of another of said regions to permit a varying of said direction, said reflecting means having a surface curved for intercepting said rays of said focusing means in a manner which retains a uniformly formed radiating aperture independently of said direction, said regions of said focusing means comprising phase shifters providing electronically selectable phase shifts, said focusing means further comprising means responsive to a beam steering command signal for generating phase shifter control signals for selecting the phases of said phase shifters, said signal generating means comprising means for computing the values of phase shifts to be selected for each of said phase shifters to direct said rays of radiant energy in the direction corresponding to said beam steering command, said signal generating means further com- V 14. In combination:

first means for phase shifting the phase of one ray of radiation relative to the phase of a second ray of radiation, said first means comprising an array of elements each of which accepts one of said rays and retransmits said ray with a phase shift imparted thereto, the phase shift imparted by one of said elements being independent of the phase shift imparted by a second of said elements;

second means for directing said elements of said first means to provide phase shifts resulting in divergent rays of radiation; and

third means having a conic section surface of the class of surfaces consisting of hyperboloids and ellipsoids for demagnifying the amount of said divergence of said diverging rays to form a beam of substantially collimated rays of radiation with a radiating aperture larger than the array of elements of said first means.

15. A focusing system for propagating radiation between an element of said system and a vehicle moving relative to said element, said system comprising:

first means for transmitting radiant energy toward said vehicle;

second means for receiving radiant energy;

third means responsive to said transmitted radiant energy of said first means for transmitting radiant energy from said vehicle toward said second means; and

said second means comprising:

means for gathering rays of said received energy, said gathering means having a uniformly curved surface of the class of surfaces consisting of hyperboloids and ellipsoids, said surface being larger than a cross section of a beam of said received energy for redirecting said rays of received energy along converging paths; and

an array of phasing means, each of said phasing means being positioned on said converging paths for independently providing predetermined phase shifts to rays of energy incident thereupon from said gathering means for further converging said rays towards a fixed point independently of the direction of said vehicle relative to said gathering means thereby providing for a scanning of said rays of energy, said gathering means being sufficiently curved to reduce the angle of scanning of a radiation which propagates from said gathering means to said phasing means, an arc of said curved surface lying in a plane containing a plurality of said ray directions altered by said array of phasing means.

16 A focusing system for propagating radiation between an element of said system and a vehicle moving relative to said element, said system comprising:

first means for transmitting radiant energy toward said vehicle; second means for receiving radiant energy;

third means responsive to said transmitted radiant energy of said first means for transmitting radiant energy from said vehicle toward said second means; said second means comprising:

means for gathering rays of said received energy, said gathering means having a uniformly curved surface larger than a cross section of a beam of said received energy for redirecting said rays of received energy along converging paths; and an array of phasing means, each of said phasing means being positioned on said converging paths for independently providing predetermined phase shifts to rays of energy incident thereupon from said gathering means for further converging said rays toward a fixed point independently of the direction of said vehicle relative to said gathering means, and means responsive to said data provided by said received radiant energy and to the present direction of said vehicle as determined from the present values of the phase shifts of said phasing means for computing a future direction of said vehicle.

17. The system according to claim 16 further comprising means responsive to said computing means and coupled to each of said phasing means for signalling said phasing means to provide predetermined phase shifts having values computed by said computing means.

18. The system according to claim 17 wherein said curved surface of said gathering means has a curvature in at least one dimension according to a conic section.

19. The system according to claim 17 wherein said curved surface of said gathering means is a hyperboloid of revolution, and said gathering means is a reflector of radiant energy.

20. The system according to claim 17 wherein said gathering means is positioned within the near field of said array of phasing means. ,7

21. The system according to claim 20 wherein said gathering means is located alongside a path of travel of said vehicle.

22. The system according to claim 21 wherein said signalling means provides said phasing means with additional signals differing in accordance with the temperatures of individual ones of said phasing means to compensate for the effect of said temperatures on said phasing means.

23. In combination:

first means for altering the direction of a wavefront of radiation incident thereupon by altering the phase of one ray of said radiation relative to another ray of said radiation, said first means comprising an array of phase shifting elements through which said rays of radiation propagate, the phase length of one of said phase shifting elements being variable with respect to the phase length of another of said phase shifting elements to permit a varying of said direction;

second means for altering the direction of one ray of radiation incident thereupon relative to another ray of radiation incident thereupon, said second means being positioned from said first means such that 'said rays of radiation propagate from one of said means to the other of said means;

means coupled to said phase shifting elements for generating phase shifter control signals for selecting the phase shift imparted by each of said phase 

1. A system for obtaining data relative to a source of radiation, said system comprising: first means for altering the direction of a wavefront of radiation of said source incident upon said first means by altering the phase of one ray of said radiation relative to another ray of said radiation, said first means comprising regions through which said rays of radiation propagate, the phase length of one of said regions being variable with respect to the phase length of another of said regions to permit a varying of said direction; second means for altering the direction of one ray of radiation incident thereupon relative to another ray of radiation incident thereupon, said second means being positioned from said first means such that said rays of radiation propagate from one of said means to the other of said means, said second means having a curved surface from the class of surfaces consisting of hyperboloids and ellipsoids, an arc of said curved surface lying in a plane containing a plurality of said wavefront directions altered by said first means, the amount of said altering of direction by said second means being selected in accordance with the amount of said altering of said phase by said first means in a manner which retains a uniformly formed radiating aperture independently of said direction; and third means coupled to said first means and said second means for extracting data relative to said source from said radiation.
 2. The system according to claim 1 further comprising fourth means coupled to said first means for varying the phase length of one of said regions independently of the phase length of another of said regions thereby accomplishing a scanning of radiation, said second means being sufficiently curved to reduce the angle of scanning of a radiation which propagates from said first means to said second means.
 3. A system for obtaining data relative to a source of radiation, said system comprising: first means for altering the direction of a wavefront of radiation of said source incident upon said first means by altering the phase of one ray of said radiation relative to another ray of radiation, said first means comprising regions through which said rays of radiation propagate, the phase length of one of said regions being variable with respect to the phase length of another of said regions to permit a varying of said direction; second means for altering the direction of one ray of radiation incident thereupon relative to another ray of radiation incident thereupon, said second means being positioned from said first means such that said rays of radiation propagate from one of said means to the other of said means, the amount of said altering of direction by said second means being selected in accordance with the amount of said altering of said phase by said first means in a manner which retains a uniformly formed radiating aperture independently of said direction, said second means comprising a surface having the form of a conic section of revolution about an axis, said axis of revolution coinciding with the axis of the conic section; third means coupled to said first means and said second means for extracting data relative to said source from said radiation, said data being trajectory data of said source with respect to a movement of said source relative to said system; and fourth means coupled to said first means for varying the phase length of one of said regions independently of the phase length of another of said regions, said fourth means being further coupled to said third means, said third means utilizing said trajectory data for adjusting said phase lengths of said regions to provide a receiving beam to intercept a future position of said source to receive radiation therefrom.
 4. The system according to claim 3 further comprising fifth means coupled to said first and said second means for transmitting radiation towards said source.
 5. The system according to claim 4 wherein said fifth means is coupled to said third means, said third means correlating received radiation signals with transmitted radiation signals.
 6. A focusing system comprising: first means for altering the direction of a wavefront of radiation incident thereupon by altering the phase of one ray of said radiation relative to and independently of the phase of another ray of said radiation; and second means positioned from said first means such that said rays of radiation propagate from one of said means to the other of said means, said second means altering the direction of one ray of radiation relative to another ray of radiation incident thereupon, said second means having a curved surface from the class of surfaces consisting of hyperboloids and ellipsoids, an arc of said curved surface lying in a plane containing a plurality of said wavefront directions altered by said first means, a central axis of said first means being angled with respect to an axis of said second means containing a focal point of said curved surface of said second means, the amount of said altering of direction by said second means being selected in accordance with the amount of said altering of said phase by said first means to generate a beam of radiation having a substantially uniform directivity pattern independently of the direction of propagation of said beam of radiation.
 7. The focusing system according to claim 6 wherein said first means comprises phase shifting elements responsive to phase shifter control signals while providing electronically selectable phase shifts, said focusing system further comprising means responsive to a beam steering command signal for generating said phase shifter control signals thereby accomplishing a scanning of radiation, said second means being sufficiently curved to reduce the angle of scanning of a radiation which propagates from said first means to said second means, said signal generating means comprising means for computing the values of phase shift to be selected for each of said phase shifters to direct said rays of radiation in the direction corresponding to said beam steering command.
 8. The focusing system according to claim 6 wherein said first means comprises phase shifting elements responsive to phase shifter control signals for providing electronically selectable phase shifts, said focusing system further comprising means responsive to a beam steering command signal for generating said phase shifter control signals thereby accomplishing a scanning of radiation, said second means being sufficiently curved to reduce the angle of scanning of a radiation which propagates from said first means to said second means, said signal generating means comprising means providing a set of pulse signals each of which is adapted to obtain a predetermined phase shift of said phase shifters, and means responsive to said values of phase shift computed by said computing means for coupling specific ones of said pulse signals to individual ones of said phase shifters.
 9. In combination: means for reflecting radiant energy; a source of radiAnt energy; and means for focusing rays of said radiant energy of said source and directing said focused rays in a direction toward said reflecting means, said focusing means comprising regions through which said rays of radiant energy propagate, the phase length of one of said regions being variable with respect to the phase length of another of said regions to permit a varying of said direction, said reflecting means having a surface curved from the class of surfaces consisting of hyperboloids and ellipsoids for intercepting said rays from said focusing means in a manner which retains a uniformly formed radiating aperture independently of said direction, an arc of said curved surface of said reflecting means lying in a plane containing a plurality of said ray directions altered by said first means.
 10. The combination according to claim 9 wherein said regions of said focusing means comprise phase shifters providing electronically selectable phase shifts thereby accomplishing a scanning of said rays of radiant energy, said reflecting means being sufficiently curved to reduce the angle of scanning of a radiation which propagates from said focusing means to said reflecting means, said focusing means further comprising means responsive to a beam steering command signal for generating phase shifter control signals for selecting the phase of said phase shifters.
 11. The combination according to claim 9 wherein said regions of said focusing means comprise phase shifters providing electronically selectable phase shifts thereby accomplishing a scanning of said rays of said radiant energy, said reflecting means being sufficiently curved to reduce the angle of scanning of a radiation which propagates from said focusing means to said reflecting means, said focusing means further comprising means responsive to a beam steering command signal for generating phase shifter control signals for selecting the phase of said phase shifters, said signal generating means comprising means for computing the values of phase shift to be selected for each of said phase shifters to direct said rays of radiant energy in the direction corresponding to said beam steering command.
 12. The combination according to claim 9 wherein said regions of said focusing means comprise phase shifters providing electronically selectable phase shifts thereby accomplishing a scanning of said rays of radiant energy, said reflecting means being sufficiently curved to reduce the angle of scanning of the radiation which propagates from said focusing means to said reflecting means, said focusing means further comprising means responsive to a beam steering command signal for generating phase shifter control signals for selecting the phases of said phase shifters, said signal generating means comprising means for computing the values of phase shifts to be selected for each of said phase shifters to direct said rays of radiant energy in the direction corresponding to said beam steering command, said signal generating means further comprising means providing a set of pulse signals each of which is adapted to select a predetermined phase shift of said phase shifters, and means responsive to said values of phase shift computed by said computing means for coupling specific ones of said pulse signals to individual ones of said phase shifters.
 13. In combination: means for reflecting radiant energy; a source of radiant energy; means for focusing rays of said radiant energy of said source and directing said focused rays in a direction towards said reflecting means, said focusing means comprising regions through which said rays of radiant energy propagate, the phase length of one of said regions being variable with respect to the phase length of another of said regions to permit a varying of said direction, said reflecting means having a surface curved for intercepting said rays of said focusing means in a manner which retains a uniformly formed radiating aperture independently of said direction, said regions of Said focusing means comprising phase shifters providing electronically selectable phase shifts, said focusing means further comprising means responsive to a beam steering command signal for generating phase shifter control signals for selecting the phases of said phase shifters, said signal generating means comprising means for computing the values of phase shifts to be selected for each of said phase shifters to direct said rays of radiant energy in the direction corresponding to said beam steering command, said signal generating means further comprising means providing a set of pulse signals each of which is adapted to select a predetermined phase shift of said phase shifters, and means responsive to said values of said phase shift computed by said computing means for coupling specific ones of said pulse signals to individual ones of said phase shifters, said signal generating means further providing additional pulse signals for temperature compensation of said phase shifters.
 14. In combination: first means for phase shifting the phase of one ray of radiation relative to the phase of a second ray of radiation, said first means comprising an array of elements each of which accepts one of said rays and retransmits said ray with a phase shift imparted thereto, the phase shift imparted by one of said elements being independent of the phase shift imparted by a second of said elements; second means for directing said elements of said first means to provide phase shifts resulting in divergent rays of radiation; and third means having a conic section surface of the class of surfaces consisting of hyperboloids and ellipsoids for demagnifying the amount of said divergence of said diverging rays to form a beam of substantially collimated rays of radiation with a radiating aperture larger than the array of elements of said first means.
 15. A focusing system for propagating radiation between an element of said system and a vehicle moving relative to said element, said system comprising: first means for transmitting radiant energy toward said vehicle; second means for receiving radiant energy; third means responsive to said transmitted radiant energy of said first means for transmitting radiant energy from said vehicle toward said second means; and said second means comprising: means for gathering rays of said received energy, said gathering means having a uniformly curved surface of the class of surfaces consisting of hyperboloids and ellipsoids, said surface being larger than a cross section of a beam of said received energy for redirecting said rays of received energy along converging paths; and an array of phasing means, each of said phasing means being positioned on said converging paths for independently providing predetermined phase shifts to rays of energy incident thereupon from said gathering means for further converging said rays towards a fixed point independently of the direction of said vehicle relative to said gathering means thereby providing for a scanning of said rays of energy, said gathering means being sufficiently curved to reduce the angle of scanning of a radiation which propagates from said gathering means to said phasing means, an arc of said curved surface lying in a plane containing a plurality of said ray directions altered by said array of phasing means.
 16. A focusing system for propagating radiation between an element of said system and a vehicle moving relative to said element, said system comprising: first means for transmitting radiant energy toward said vehicle; second means for receiving radiant energy; third means responsive to said transmitted radiant energy of said first means for transmitting radiant energy from said vehicle toward said second means; said second means comprising: means for gathering rays of said received energy, said gathering means having a uniformly curved surface larger than a cross section of a beam of said received energy for redirecting said rayS of received energy along converging paths; and an array of phasing means, each of said phasing means being positioned on said converging paths for independently providing predetermined phase shifts to rays of energy incident thereupon from said gathering means for further converging said rays toward a fixed point independently of the direction of said vehicle relative to said gathering means, and means responsive to said data provided by said received radiant energy and to the present direction of said vehicle as determined from the present values of the phase shifts of said phasing means for computing a future direction of said vehicle.
 17. The system according to claim 16 further comprising means responsive to said computing means and coupled to each of said phasing means for signalling said phasing means to provide predetermined phase shifts having values computed by said computing means.
 18. The system according to claim 17 wherein said curved surface of said gathering means has a curvature in at least one dimension according to a conic section.
 19. The system according to claim 17 wherein said curved surface of said gathering means is a hyperboloid of revolution, and said gathering means is a reflector of radiant energy.
 20. The system according to claim 17 wherein said gathering means is positioned within the near field of said array of phasing means.
 21. The system according to claim 20 wherein said gathering means is located alongside a path of travel of said vehicle.
 22. The system according to claim 21 wherein said signalling means provides said phasing means with additional signals differing in accordance with the temperatures of individual ones of said phasing means to compensate for the effect of said temperatures on said phasing means.
 23. In combination: first means for altering the direction of a wavefront of radiation incident thereupon by altering the phase of one ray of said radiation relative to another ray of said radiation, said first means comprising an array of phase shifting elements through which said rays of radiation propagate, the phase length of one of said phase shifting elements being variable with respect to the phase length of another of said phase shifting elements to permit a varying of said direction; second means for altering the direction of one ray of radiation incident thereupon relative to another ray of radiation incident thereupon, said second means being positioned from said first means such that said rays of radiation propagate from one of said means to the other of said means; means coupled to said phase shifting elements for generating phase shifter control signals for selecting the phase shift imparted by each of said phase shifting elements, said signal generating means comprising means for providing a set of pulse signals each of which is adapted to select a predetermined phase shift of said phase shifters and means for providing additional pulse signals to each of said phase shifting elements in accordance with its location in the array of said phase shifting elements for temperature compensation of said phase shifters.
 24. In combination: first means for altering the direction of a wavefront of radiation incident thereupon by altering the phase of one ray of said radiation relative to another ray of said radiation, said first means comprising regions through which said rays of radiation propagate, the phase length of one of said regions being variable with respect to the phase length of another of said regions to permit a varying of said direction thereby accomplishing a scanning of radiation; and second means for altering the direction of one ray of radiation incident thereupon, said second means being positioned within the Fresnel zone of said first means such that said rays of radiation propagate from one of said means to the other of said means, said second means having a curved surface of the class of surfaces consisting of hyperboloids and ellipsoids, a central axis of said first means being angled with respect to an axis of said second means containing a focal point of said surface, an arc of said curved surface lying in a plane containing a plurality of said wavefront directions altered by said first means, said second means being sufficiently curved to reduce the angle of scanning of a radiation which propagates from said first means to said second means. 